As the minimum feature sizes of semiconductor devices decrease and the spacing of the adjacent metal lines decreases, reliability problems such as failing Highly Accelerated Temperature/Humidity Stress Test (HAST), increasing electromigration and stress migration become more serious. Shrinking of device dimensions and scaling down of metal spacing and width cause higher resistance and current density. Higher current density can increase the rate at which metals grow metallic dendrites that reduce the spacing between the adjacent metal lines and eventually create a short.
One way to prevent interconnect failure from such shorts from occurring is to increase metal spacing. Increasing metal spacing is impractical because devices will continue to shrink. As an alternative, metal bridge shorts can be reduced by applying various surface treatments to the metal, e.g., exposing the metal layer to ammonia (NH3) has been found to reduce metal diffusion along that interface. Introducing dopants into the metal layer also limits diffusion. Unfortunately, these techniques for reducing the rate at which metal diffuses raise the resistance of the metal layer significantly.
Accordingly, there is a need for a novel structure or an improved process for making a semiconductor device that includes metal interconnects. There is a need for such a novel structure or a process that reduce the metal bridge. The present invention provides such a novel structure and a process.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to illustrate the relevant aspects of various embodiments and are not drawn to scale.